In semiconductor integrated circuit (IC) industry, technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of IC processing and manufacturing.
A photolithography process forms a patterned resist layer for various patterning processes, such as etching or ion implantation. The minimum feature size that may be patterned by way of such a lithography process is limited by the wavelength of the projected radiation source. Lithography machines have gone from using ultraviolet light with a wavelength of 365 nanometers to using deep ultraviolet (DUV) light including a krypton fluoride laser (KrF laser) of 248 nanometers and an argon fluoride laser (ArF laser) of 193 nanometers, and to using extreme ultraviolet (EUV) light of a wavelength of 13.5 nanometers, improving the resolution at every step.
In the photolithography process, a photomask (or mask) is used. The mask includes a substrate and a patterned layer that defines an integrated circuit to be transferred to a semiconductor substrate during the photolithography process. The mask is typically included with a pellicle assembly, collectively referred to as a mask-pellicle system. The pellicle assembly includes a transparent thin membrane and a pellicle frame, where the membrane is mounted over the pellicle frame. The pellicle assembly protects the mask from fallen particles and keeps the particles out of focus so that they do not produce a patterned image, which may cause defects when the mask is being used. Pellicle assemblies for EUV lithography have proved challenging to fabricate and implement, due at least in part to the difficulty of providing a thin pellicle membrane with sufficient structural integrity to span the surface of the mask. The fabrication of large, thin pellicle membranes according to certain conventional fabrication processes has been shown to cause the pellicle membrane to become distorted, wrinkled, broken, or otherwise damaged, thereby rendering the pellicle membrane unusable.
Thus, existing techniques for fabricating mask-pellicle systems have not proved entirely satisfactory in all aspects.